1. Field of the Invention
This invention relates to a method of fabricating semiconductor devices exhibiting a low thermal resistance, and the devices obtained thereby. More particularly, this invention relates to diodes and transistors which it is desired to isolate electrically from ground, while still providing for good elimination of the calories dissipated in the active layers of the semiconductor device.
2. Description of the Prior Art
One method used up to now to obtain the above result consists of inserting a slab of beryllium oxide between the substrate of the device and the metallic support, generally copper, serving as heat sink. Knowing that the energy dissipation in the diodes and transistors takes place at the active layers at a shallow depth in the substrate (5 to 15 microns), the thicknesses of material entering into the calculation of the thermal resistance are, for example, as follows:
100 TO 150 MICRONS FOR THE SUBSTRATE OBTAINED GENERALLY BY CUTTING UP A DISK OF SEMICONDUCTOR MATERIAL WHICH SHOULD BE OF A THICKNESS COMPATIBLE WITH THE MINIMAL SOLIDITY REQUIRED FOR MANIPULATION;
600 MICRONS AT LEAST FOR THE SLAB OF BERYLLIUM OXIDE WHICH CAN BE NO THINNER WITHOUT COMPROMISING THE SOLIDITY OF THE SLAB AND RISKING BREAKAGE DURING ASSEMBLY.
Beryllium oxide is known to have a thermal conductivity about three times greater than that of a semiconductor material such as silicon. The total thickness to take into consideration in calculating the thermal resistance is thus, in the case examined above, equivalent to about 300 to 350 microns of silicon. A thickness of this order contributes to appreciable limitation of the power-handling performance of the device.